1. Field of the Invention
This invention relates to a method of producing Fe-Ni series alloys having an improved effect of restraining streaks during the etching, and more particularly to a method of producing Fe-Ni series alloys suitable as a material for use in an electronic equipment such as a shadow mask for color television cathode tube, an electron-ray indicator tube or the like.
2. Related Art Statement
Iron-nickel series alloys (hereinafter abbreviated as Fe-Ni alloy) used as a material for a shadow mask of a color television cathode tube are pointed out to have a drawback that a white stringer pattern or so-called streak is caused in the production of the shadow mask through photoetching.
As a technique for restraining the streaks during the etching, there have hitherto been proposed the following methods. For example, Japanese Patent laid open No. 60-128,253 discloses a method of controlling the occurrence of streaks, wherein an ingot is usually heated above 850.degree. C. and forged at a total sectional reduction ratio of not less than 40% per one heat to mitigate the segregation portion of nickel.
Furthermore, Japanese Patent laid open No. 61-223,188 discloses a method of restraining the occurrence of streaks, wherein the segregation ratio of nickel and the segregation zone thereof are controlled by the prevention of segregation in the production of ingots or by subjecting the nickel to a diffusion treatment through a heat treatment in the production step of bars.
However, the conventional technique disclosed in Japanese Patent laid open No. 60-128,253 is concerned with a method of conducting the forging at the total sectional reduction ratio of more than 40%, but the segregation of various elements cannot be substantially restrained since such a forging is under an usually used loading. As a result, it is not possible to prevent the occurrence of streaks during the etching.
On the other hand, the technique disclosed in Japanese Patent laid open No. 61-223,188 shows a method of mitigating the component segregation through the diffusion of Ni based on high-temperature heat treatment. However, since the sheet thickness is thin as compared with the case of heating at the slab stage, the oxidation loss becomes relatively large and the yield is considerably and undesirably lowered.
In these techniques, the ingot is usually used as a starting material. Now, the solidification structure of the starting material does not come into problem, but the yield of a product is low and the cost is high since the starting material is supplied in form of an ingot.
As mentioned above, these conventional techniques can not completely prevent the occurrence of streaks during the etching, or can not produce cheap products industrially.